Fun idea, but...
Given the mass and unpredictable actions of the passengers and therefore the probability of their affecting the trajectory of the cars, bad idea (unless you come up with some invisible means of reliably controlling the motion of the coaster cars while mechanically disconnected from the track).

Having the roller coaster completely leave the track might make for a nice zero-G experience if everything worked out just perfectly, but something would almost certainly go wrong.

On the other hand, it might be interesting to design a suspended roller coaster whose cables would be slack for part of the ride. Some careful engineering would be necessary to ensure that under all scenarios the positions, forces, and accellerations of all parts of the system remained within acceptable limits, but if properly done the overall effect could be really cool.

Hey, the (perceived potential for) things to go wrong is half the fun..

I'm not sure that weight differences would be a problem (all objects accelerate at the same rate - neglecting air friction). If air friction was non-negligable I suppose you could weigh the train and add ballast.

I was imagining some form of 'funnel' to catch the train and re-track the wheels. Alternatively (or possibly in addition) I suppose you could have a sort of catching hook which would reach out and grab the front of the train and lead it to the right place for a gradual contact, while still basically following parabolic flight.

I'm not sure the jump would actually be that noticable, as people say it would be maybe a few seconds of zero-G. I think the main payoff would be actually seeing the train jump while you were queueing and building anticipation.

Speaking of RTC, I've found that a great moneymaker is a catapult-launch coaster which has the loading platform built as high as possible on the tallest allowable hill, then goes into the deepest allowable valley, and then climbs to the tallest allowable height. Put two of them next to each other and you'll end up with a very high thrill rating and minimal nausea rating on a ride that is very short and can thus serve a huge number of people.

Another fun little detail of RTC: if a ride exit is underground and there's no tunnel there or underneath it, people exiting the ride will simply disappear. They won't register as dying--they'll just vanish altogether. If one was unscrupulous, one could construct a 'prison' with such a ride in it (ride price: free), and drop unhappy park guests there so as to boost the average happiness rating.